The present invention relates to a sound editor which edits an audio signal using one or more audio signals as its sound sources.
A audio sound editor which handles only a digital sound signal as its source has been suggested.
FIG. 1 illustrates the structure of the main part of such digital sound editor 10. Reference numeral 12 denotes a player such as a MO player, a PCM player, a VCR, a DAT player, or a CD player providing the source, the audio signal of which has been digitally recorded in advance.
The sources have time codes TC pre-recorded together with the digital audio signals. Based on the time code TC, the sound editor 10 allows non-linear editing in which sources can be selected at random.
The player 12 reproduces the sources which may used for editing and which are thereafter recorded as audio material for editing in a hard disk drive (HDD) 40.
FIG. 2 illustrates an example of an editing list which includes editing information such as the order of reproduction, information about the audio material to be used, and cut points. Based on such editing information, an audio signal edited from such cuts can be produced as shown in FIG. 3A.
When performing a programmed reproduction according to the editing list, a DSP (digital signal processor) 20 for processing the audio signals reads from the HDD 40 and performs specific signal processes (filtering, cross-fading and so on). The DSP 20 has a DSP block 21 and a RAM 22 as its working memory as shown in FIG. 1.
The edited audio signal reproduced by the programmed operation is provided to a speaker (not shown) or is recorded by a recording device 42 such as a MO recorder or a PCM recorder. The recorder 42 can also record the editing list together with the audio signal.
The editing list includes editing points and signal processing information (filtering characteristics, gradient data for cross-fading, and so on). The editing list is used to re-arrange the order of the cuts in FIG. 3A into the order in FIG. 3B.
In the editing operation, a reproduction based on the editing list (a programmed reproduction) is repeated and checked, until a final editing list is produced, at which point the editing operation is completed. In the editing list, the cross-fading process is performed for every cut in real time simultaneously with editing and verification, and at such time, the problem described below occurs.
The non-linear editing includes an operation for replacing a single sound. For instance, it is necessary to replace a sound (or some sounds) with another (or others) when the sound from the source is off pitch or is accidentally mixed with noise in a fragment of time. In this case, the length of the cut to be edited may be extremely short.
Referring to FIG. 4, when two RAMs 22a and 22b are used as the DSP memory 22, a read operation and a write operation are performed alternately. When instructed to access a specific cut, that cut is read from the HDD 40 and the next cut must be accessed prior to the time the first cut has been completely written into the RAM 22a or 22b; thus, the file information just prior to the next cut cannot be totally recorded.
Minimum time T(msec.) is the time that is required for the memory process for the HDD, and so forth, starting form the time the access is begun, the data is written in using a different memory process and the writing is completed, until it is possible to begin the next process, together with a little leeway.
Referring to FIG. 5, when the length (time) of a cut A2 is below the minimum time T (300 msec. to 2 sec. in general), the cut A2 cannot be recorded correctly because the access to the cut A3 starts before cut A2 is entirely recorded. In this way, the editing operation is not completely performed and an interruption in sound results. Such interruption in sound often occurs in the editing operation for replacing a single sound.